System for the continuous and automatic measurement of the sulfur content of petroleum fractions



KElsHl HSBGAWA ET AL 3,500,446

March l0, 1970 SYSTEM FOR THE CONTINUOUS'ND AUTOMATIC MEASUREMENT'OF Filed Fb.- 14,v 196B THE. SULFUl CONTENT OF PETROLEUM FRACTIONS .k SLS NN 4 United States Patent U.S. Cl. Z50- 43.5 5 Claims ABSTRACT F THE DISCLOSURE A system for continuously and automatically measuring the sulfur content of petroleum products continuously flowing through a pipe having an X-ray sample cell, a beta ray sample cell provided in association with the pipe, an X-ray source and X-ray detector on opposite sides of the X-ray sample cell, a beta ray source and a beta ray detector on opposite sides of the beta ray sample cell, a metal foil positioned between said beta ray source and said beta ray sample cell and a computer connected to said detectors for receiving separate signals therefrom indicating the transmission intensities of the sample by X- rays and beta rays, respectively, said computer being operative to provide an output signal indicative of the sulfur content of the sample and means responsive to said output signal for continuously and automatically indicating the Sulfur content calculated with said computer.

This application is a continuation-in-part of our\pending application Ser. No. 518,358, filed I an. 3, 1966, now abandoned.

This invention relates to a system for continuously, automatically, accurately and quickly measuring and analyzing the sulfur content of petroleum products during the flow of products in a process of refining petroleum or a process of mixing petroleum products and, more particularly, it relates to a system for automatically and continuously calculating and indicating the sulfur content by means of circuitry capable of detecting the penetrabilities of petroleum samples by two kinds of radiation sources, namely, X-rays and beta rays.

As is well known, almost all petroleum fractions contain sulfur. However, generally, the presence of elemental sulfur and sulfur compounds in petroleum products is undesirable. Therefore, a considerable part of the sulfur must be removed by suitable desulfurization treatments and the sulfur content of petroleum products must always be kept under strict control. It is therefore evident that, if the sulfur content of petroleum products can be continuously, automatically, accurately and quickly measured as the products flow through the refining or mixing processes so that steps can be taken, if necessary, to maintain the sulfur content within suitable values, it will be possible to improve greatly the quality of the products, to reduce the operating costs and to prevent the production of faulty products.

Previously there have been suggested many methods of measuring the sulfur content of petroleum products. Suitable procedures are mentioned in various publications of the ASTM, IP and JIS. However, such procedures, which generally involve combustion steps, generally require a long time and considerable skill and, therefore, are not adapted to achieve the objects of the present invention. Further, recently there have been developed methods of measuring the sulfur content of petroleum products -by using radioactive isotopes. For example, there is known a method of calculating sulfur content from a value of ICC ` density of the petroleum product measured by a separate means and from the amount of X-rays absorbed by the petroleum product, utilizing the property that X-rays emitted from 55Fe, 3H or 1WPm are absorbed by sulfur much more than by hydrogen and carbon, which are principal constituents of petroleum. The measurement of density has been made by batch procedures, such as by placing a sample into a cylinder and measuring its density with a hydrometer. However, needless to say, it is impossible to incorporate such a measurement into a continuous petroleum refining process to obtain a continuous measurement. In this connection, there is already known a density-compensating-type, sulfur content measuring method wherein density compensation is made by a mechanical process by utilizing the variation of the height of a liquid surface by the density variation of a sample caused when a predetermined weight of a petroleum fraction is taken into a particular sample container. In such method, the response time of the density compensation measurement of a petroleum fraction of a high viscosity is so slow and the measured value has so many errors that it is impossible to quickly measure the sulfur content as the petroleum ows, using an apparatus adapted to measure selected portions of the petroleum stream.

The object of the present invention is to improve such sulfur content measuring methods and to make it possible .to accurately measure the sulfur content of petroleum products, even petroleum products of a high viscosity, and to continuously, automatically, accurately and quickly measure the sulfur content generally with an apparatus adapted to be applied to a continuously flowing stream of petroleum products.

According to the present invention, it is possible to quickly provide measured sulfur content values of high accuracy, using a sulfur content measuring apparatus which is small and light, by relating the absorption of X- rays and the absorption of beta rays by the petroleum produ-cts with each other. It is very simple to incorporate the measuring system of the present invention into any lpetroleum refining apparatus. For X-ray sources there can be used 55Fe, 3H and 11'7Pm. The absorption of X-rays will be influenced by the density, sulfur content and carbon/hydrogen ratio of the sample. For beta ray sources there can be used 90Sr and 144Ce. The absorption of beta rays will -be influenced by the density and carbon/hydrogen ratio of the sample but same `will not `be influenced by the sulfur content. Further, the variation lof the carbon/ hydrogen ratio in a petroleum fraction in any given process of petroleum refinement is so small that only the variation of density need be taken into consideration in relation to the compensation for the absorption value of X- rays. The apparatus of the present invention is characterized by using a beta ray source as a means of such density compensation. If any other radiation source such as, for example, a gamma radiation source, is used the size of the sample required to measure the gamma ray absorption will be far larger than in the case 'of beta rays. Therefore, not only the apparatus itself will have to be made so large as to be inconvenient to handle, but also a sample will be required which is of much larger size than the sample needed for the X-ray measurement. Thus, a time lag will occur in the measurement and the measured value Will have errors. Therefore, in the present invention, a beta ray source is used for density compensation. However, if this beta radiation source is directly applied to the petroleum product, the density of the petroleum product cannot be measured accurately because the beta rays will be greatly influenced by the carbon/hydrogen ratio. In this connection, we have discovered that if the beta rays are shielded by a metal foil of a thickness of 20 to mg./cm.2 or preferably 30 to 50 mg./crn.2, beta rays can be used effectively. It is preferred that the metal foils be made of tin, aluminum or cadmium. For example, if guSr is shielded with an aluminum foil of 40 mg./cm.2 thickness, the inuence of the carbon/hydrogen ratio in the density measurement will be reduced to one-tenth as much as when there is no shield. Further, thereby the density can be represented by a linear formula of the beta ray penetrability and density compensation can be simply made.

In the present invention, a sample cell to be transmitted by X-rays is made of an anticorrosive metal and has an X-ray penetrable part or `window made of a -beryllium plate. The proper transmitted thickness of the sample cell is from 2 to 6 mm., preferably 3 to 4 mm. The strength of the X-ray source is more than 4 millicuries, usually 5 millicuries for 55Fe.

The proper transmitted thickness of the sample cell for kbeta rays is from 2 to 10 mm., preferably 4 to 5 mm. The strength of the beta ray source is from 0.5 to 5 millicuries, usually 2 millicuries.

From many experimental values, we have determined by the method of least squares that the logarithm of the intesity of the X-ray transmission (I) of any given petroleum sample is represented approximately by a linear formula based on the density ((p) of the sample, the carbon/ hydrogen ratio (C/ H of the sample and the sulfur content (percent S) of the sample and that the logarithm of the intensity of the beta ray transmission (I) of a sample is represented approximately by a linear formula based on the density (o) and the carbon/hydrogen ratio (C/H) of the sample. That is to say, we have found experimentally that the transmission intensities can be represented vby the following equations:

1.3286 log I-log I-0.837 C'/H-6.583

which could be represented by the following general equation:

Percent S K1 log I-log I-K2R K3 wherein R=C/H and K1, K2, K3 and K4 are constants.

In the apparatus of the present invention, the values of the transmission intensities I and I', obtained with an X-ray detector and a beta ray detector, respectively, as described above, are introduced into an operation circuit which is constructed so as to operate in accordance with the above-mentioned Formula (l), and this operatoin circuit is connected to a sulfur content indicator so that the sulfur content in the sample may be automatically and continuously indicated. If an automatic recorder is connected to the circuit, the sulfur content will be able to be automatically recorded.

That is to say, the present invention provides a system for continuously and automatically measuring the sulfur content of petroleum products, which system comprises an X-ray transmission sample cell and a beta ray transmission sample cell provided in a pipe through which a sample flows. An X-ray source and an X-ray detector and a beta ray source and a beta ray penetrability detector are provided in association with the respective sample cells and a shielding metal foil of a thickness of to 80 mg./cm.2 is positioned between the beta ray source and its associated sample cell. The two detectors are connected to an operation circuit for calculating the sulfur content of the sample from the X-ray transmis- Percent S sion intensity and beta ray transmission intensity through the sample so that the sulfur content calculated with said circuit may be indicated by a sulfur content indicator and recorder connected to said circuit.

The apparatus and method of the present invention shall be explained in the following with reference to the accompanying drawing in which:

FIGURE 1 is a schematic block diagram of the system.

FIGURE 2 is a central sectional View through the `beta ray cell.

In the drawing, 1 and 2 are ray source containers each having a collimator in the direction of permeating a petroleum fraction. An X-ray source and a beta ray source are respectively provided in them.

The radioactive rays radiated from the ray sources 1 and 2 will permeate sample cells 3 and 3 and will enter radioactive ray detectors, for example, Geiger Mueller counter tubes 6 and 7, respectively.

At the time of measurement, an oil to be measured is made to continuously flow to the sample cells 3 and 3. (The thicknesses of the sample cells in the radioactive ray permeating direction shall be respectively d and d.)

4 is a standard absorbent. With the sample cells 3 and 3' empty, the standard absorbent is positioned in the radioactive ray permeating path and a standard indication is set in a recorder 21. A K3 setting circuit 17 is adjusted and coupled to the recorder so that a correction can be made for the respective half-life periods of the ray sources. An aluminum plate is used as the standard absorbent, for example.

In the Geiger Mueller tubes, each radioactive ray is converted to a pulse-shaped electric signal. The radio-active ray detector outputs are fed to impedance converters 8 and 9. By this means, electric signals of high output impedances from the Geiger Mueller tubes 6 and 7 can be transmitted over a long distance. 10 and 11 are socalled logarithmic counting rate meters from which the outputs are direct currents which are proportional to the logarithmic values of the numbers per unit time of pulseshaped electric signals from the impedance converters 8 and 9, respectively. That is to say, the outputs of meters 10 and 11 correspond to the factors log I and log I in the Formula. l. 12 and 13 are direct current amplifiers which can well amplify the output signals of the logarithmic counting rate meters 10 and 11, respectively. The outputs of amplifiers 12 and 13, for example, direct currents il and i2. The total conversion constants of a the logarithmic counting rate meter 10 and direct current amplifier 12 and b the logarithmic counting rate meter 11 and direct current amplifier 13, are made exactly the same.

The above-described direct currents i1 and i2 are fed respectively to electric resistors 15 (of a resistance r1) and 14 (of a resistance r2) so that direct current voltages e2 and e1 may be respectively generated at both ends. Here, the ratio of 1'2/11 is made proportional to K1 in the Formula 1. The direct current voltages e1 and e2 are connected together by conductor 20 so that their polarities may `be reverse to each other. If e3 is obtained, it Will be direct current voltage proportional to (K1 log I-log I) in the Formula 1.

16 is a circuit for generating a direct current voltage e4 proportional to KZR in the Formula 1. The proportion constant between e4 and KZR is made exactly the same as the proportion constant between e3 and (K1 log 1log I The `KyR setting circuit 16 can be made manually variable in response to C/ H of the petroleum fraction flowing to the sample cells. 17 is a circuit for generating a direct current voltage e5. proportional to K3 and the proportion constant is the same as in the case of e4. As shown in FIGURE l, the KZR setting circuit 16 and K3 setting circuit 17 are connected in series so that the polarities of the generated voltages e4 and e5 may be in the same direction as of e3 according to the Formula 1. The voltage e6 is equal to the sum of e3, e4 and e5 and is proportional to the numerator of the Formula 1.

As K., in the Formula 1 is a constant, e6 will be proapparatus according to the present invention has numerous advantages, such as, it includes no division circuit, only two simple ampliers are used, the for-mation construction of the circuit is simple and the number of parts is small. Therefore, `the maintenance of the apparatus is easy and the errors of the apparatus are small.

Further, stability of the apparatus can be easily obtained and manufacture of the apparatus at a low cost is possible. Therefore, it is possible to satisfy all of the features of precision, stability and maintenance required in industrially usable measuring devices.

Further, the correction for the damping of the ray source is also =Very simple. The K3 setting circuit 17 may be adjusted so lthat the output per-meating through the standard absorbent, for example, the. aluminum plate, may be of a predetermined value (by setting in advance the standard indication when the standard absorbent is inserted into the recorder). The same method can be used to correct not only the damping of the ray source but also the displacement of the position of the ray source, the variation of the detector output and the displacement of the position of the detector.

Since the various circuit elements for the K2R, K3 and K4 circuits and logarithmic converting operations are well known to persons acquainted with analog computing circuits and since such elements are not part of this invention, they will not be further described herein.

It has been found acceptable to use, as the impedance couver-ters 8 and 9, Type PC-8 impedance converters manufactured by Hokushin Electric Works, Ltd. of Kobe, Japan. The log counting rate meters 10 and 11 may be Type RM-4 rate meters made by the same manufacturer.

Referring to FIGURE 2, the sample cell 3 has a beta ray source 21 associated therewith for directing beta rays through the cell toward the detector 6. A metal foil 22 of to 80 Ing/cm.2 thickness is positioned between the beta ray source and the cell 3' in order to minimize the effect of variations in the C/H ratio in the petroleum product.

With the apparatus ofthe present invention, there can be obtained excellent results such that the accuracy of measurement of percent S is 0.06% S for a light oil of 0.25 to 1.0% S, and 0.08% S for a heavy oil of 1.0 to 3.8% S.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A system for continuously and automatically measuring the sulfur content of petroleum products passing through a pipe, comprising:

an X-ray sample cell and a beta ray sample cell provided in association with the pipe;

an X-ray source and an X-ray detectoron opposite sides of the X-ray sample cell;

a beta ray source and a beta ray detector on opposite sides of the beta ray sample cell;

a metal foil positioned between said beta ray source and said beta ray sample cell;

an operation circuit which is constructed so as to operate in accordance with the following formula:

wherein percent S is the sulfur content of the sample, I and I are the X-ray and beta ray transmission intensities of the sample respectively, R is the carbon/hydrogen ratio of the sample and K1, K2, K3 and K4 are constants, said circuit being connected to said detectors for receiving separate signals therefrom indicating the transmission intensities of the sample by X-rays and beta rays, respectively, said circuit being operative to provide an output signal indicative of the sulfur content of the sample and means responsive to said output signal for continuously and automatically indicating the sulfur content calculated with said operation circuit.

2. A system according =to claim 1, wherein said X-ray source is a member selected from the group consisting of Fe, 3H and 147Pm.

3. A system according to claim 1, wherein said beta ray source is a member selected from the group consisting of Sr and 144Ce.

4. A system according to claim 1, wherein said metal foil is a member selected from the group consisting of tin, aluminum and cadmium foils.

5. A method according to claim 1, wherein the thickness of said metal foil is 20 to 80 Ing/cm?.

Percent S References Cited UNITED STATES PATENTS 2,937,275 5/ 1960 T hourson et al. 3,254,214 5/ 1966 Bennett. 3,255,975 6/1966 Malin et al. 3,280,327 10/1966 Amrehn.

ARCHIE R. BORCHELT, Primary Examiner 

